Asphalt-rubber compositions have been found to be a new and useful pavement material for surfacing and manufacturing roadways, and for repairing cracked roadways and pavements. Such compositions are generally applied by spraying and are difficult to spray because of their high viscosity. Heat may be used to decrease the viscosity but this requires special equipment and experienced personnel in working with the hot material on the job site. Organic solvents may be used to cut such compositions to decrease their viscosity but this adds to the cost of the composition and presents additional problems associated with the handling of organic solvents especially with hot compositions.
Asphalt-rubber compositions have also been applied in the form of a water emulsion which is pourable and sprayable under ambient temperatures. Upon application of such emulsion, the emulsion breaks and the asphalt-rubber composition is deposited on the roadway. Aqueous emulsions of asphalt are known in the art and have been found to be stable and easily pourable and sprayable. A difficulty, however, has been experienced while attempting to emulsify asphalt-rubber compositions containing particulate rubber in that the emulsion tends to "break" or separate upon standing. This is believed to be due to the presence of sulfur in the rubber used in preparing the asphalt-rubber compositions.
In an effort to stablize such emulsions, emulsifiers such as clays and talc have been added to the emulsion to improve their stability. Such emulsifiers do provide for stability but their presence in the emulsion after application to a roadway or pavement presents a risk that the composition will re-emulsify under the action of water and traffic with a consequent washing away of the composition. The presence of such clays and talc also inhibit the initial adhesion of the rubber-asphalt composition to stone aggregate used therewith.
The aforesaid problems have been solved by the method and emulsion described in my Patent, U.S. Pat. No. 4,018,730, which discloses the use of a specially prepared anionic soap to achieve a stable emulsion. Emulsions made with this anionic soap, however, are limited to use with stone aggregate, such as limestone, which has a cationic surface charge. If used with siliceous stone aggregate having an anionic surface charge, such as granite or quartzite, the electrical repulsion prevents a quick adhesion between the aggregate and the asphalt-rubber composition and thereby tends to prevent the emulsion from breaking quickly when applied to a roadway. The asphalt-rubber composition, which is still in an emulsified condition, may therefore be washed away when subjected to the action of rain and traffic. When the electrical charge between the aggregate and the emulsion is of different polarity, the emulsion breaks immediately due to this electrical attraction and the asphalt-rubber composition adheres immediately to such aggregate. The possibility of the asphalt-rubber composition being washed-off the aggregate is thereby eliminated.
It is therefore an object of the present invention to provide a new method for emulsifying asphalt-rubber paving compositions to provide an emulsion that is stable and will not break or settle-out upon storage, and which can be used with stone aggregate having an anionic surface charge. Another object is to provide an emulsified asphalt-rubber paving composition which will not re-emulsify after deposition. Other objects and advantages of the invention will become apparent as the specification proceeds.